The present invention relates to the field of fluid screening systems and in particular, discloses an improved form of screening especially useful for screening materials from fluids in stormwater and storm overflow, water reservoirs, dams, pump stations, wastewater and water treatment plants including by-pass flows, fluid wastes and dissipation of the kinetic energy of the flows to a point where girt can be arrested etc.
There are obviously many uses for screening systems in society. One popular use of a screening system positioned across the channel is the screening of material from a liquid stream/catchment prior to entering a receiving unit positioned downstream. Presently, known techniques rely upon a motor and geared arrangement for driving a raking mechanism (either linear or curved translation) in a vertical plane in the same plane as the screen bars which are pitched evenly and raked by tynes to collect the screenings. The rake is then driven by the motor so as to translate and thereby collect and dispose of the screenings at the end of its path in a usual manner. Alternatively, other than mechanical drives, hydraulic drive arrangements have been used.
Unfortunately, presently utilised systems have a number of disadvantages. In particular, the presently utilised systems have been found to be limited in their screening flow capacity especially during intermittent periods of abnormal loads such as heavy storms etc. The upstream liquid often backs up and breaks the sides of the channel due to the increased resistance to flow through the screen. In the case of polluted liquids this is a public health issue and breaches statute and license requirements regulated by the Environmental Protection Authority (EPA). This requires a larger size screen and respective channel/infrastructure to handle the increased screen flow thus increased costs. However, as the EPA screening requirements become more stringent, finer pitched screens are required and corresponding hydraulic difference is increased across the screen, requiring increased hydraulic differences in elevation to drive the fluid through the screen. Furthermore, the screenings capture volume is increased severely due to the finer pitched screen bars.
Another common problem is the hydraulic backwater that is created upstream of the screen may result in manhole covers being lifted off their seats due to the surcharge effect particularly in the case of gravity feed screened systems. The effects applied to screening fluids may in turn result in compromising public health and safety or provide a unit process of poor quality and efficiency.
It is therefore evident that there is a long felt need for a screening system which provides for a safer, more effective operation.
In accordance with a first aspect of the present invention, there is provided a method of dealing with an overflow capacity of a fluid screening system, the system including the first screen for screening objects of a first predetermined size from a fluid channel, the method comprising the step of: providing an ancillary screening system upstream of the screen and operational upon fluid within the channel reaching a predetermined limit, the ancillary screening system screening objects of a second predetermined size from the fluid channel.
The second predetermined size can be less than the first predetermined size.
The ancillary screening system preferably can include a screen placed substantially tangentially to the main flow of fluid within the fluid channel and includes a raking mechanism for clearing objects lodged substantially adjacent the ancillary screening system. The output of the ancillary screening system can be interconnected to the fluid channel downstream of the first screen.
In accordance with a further aspect of the present invention, there is provided an ancillary screening apparatus for screening an overflow capacity of a fluid screening system, the system including a screen for screening objects of a first predetermined size from a fluid channel, the ancillary screening apparatus including: a screening means including a second screen for screening objects of a second predetermined size from the channel upon fluid within the channel reaching a predetermined limit. The second predetermined size is preferably less than the first predetermined size.
The ancillary screening system preferably can include a raking mechanism adapted to rake the second screen so as to clear objects caught in the second screen. The screen can comprise a series of spaced apart slats and the raking mechanism preferably can include a series of tynes driven in a reciprocating manner between the slats. The raking mechanism can be located downstream of the screen. The raking mechanism preferably can include a reciprocating means comprising a gear with different offset holes located from the centre of the gear to change the stroke length of the reciprocation as the gear moves along its mating gear rack positioned parallel to the slats along the length of the screen.
The apparatus can be adapted to be located with the second screen being substantially tangential to the main flow of fluid within the fluid channel. The raking mechanism can be driven by a drive mechanism attached to an electrical actuator with the raking mechanism attached to the drive mechanism at the top and bottom of the screen. The drive mechanism preferably can include a belt drive, chain drive or worm drive.
In accordance with a further aspect of the present invention, there is provided a screening arrangement for screening fluids comprising of the frame and screen bars however, the screening bars stacked and pitched evenly in a horizontal position, a mechanically driven raking mechanism that translates horizontally with oscillating self-cleaning tynes that push the caught material off the screen bars. Also an optional high pressure jet sprays using re-use effluent can be installed in the tynes to assist in the cleaning of the screen bars as the oscillating tynes translates horizontally. A submersible IP68, class I zone I drive motor for driving the raking mechanism complete with travel position limit switches and overtorque device; a overtorque limiting mechanism for disengaging the raking mechanism from the drive motor when the linear force on the raking mechanism exceeds a first predetermined limit. A preset overflow weir is located above the screen in the event of power failure or overtorque activation to not inhibit the incoming flow.
Preferably, the screen bars are orientated stacked evenly in a horizontal position which are located within the frame of the screen, but installed and secured within the length of the wall upstream of the existing first screen. This allows an increase in hydraulic capacity of the existing channel and concentrates the screenings material to the existing first screen which lifts the material from the fluid stream.
The relative level of the lowest horizontal screen bar within its frame can be set to allow the liquid to divert or bypass its flow after a predetermined flow has reached the existing first screen installed across the channel. The screenings/coarse materials lie across the width of the horizontally stacked evenly pitched screenings bar while the fluids passes through.
Further, the mechanically driven raking system is positively driven by either a toothed timing belt, chain, inclined plane worm and thread type drive, but is sealed from the fluid stream. The drive is composed of a slider block that is guided within the horizontal legs of the frame and is positively located and positioned by either the timing belt, chain or inclined plane worm and thread drive. The legs supporting and transposing the raking tynes are positively secured to the slider block. The legs and frame are sealed to stop any moisture, grit or contamination entering the slider block guide chamber and frame.
The slider blocks transfer the linear motion from the drive train through to the tynes. The tynes reciprocate backwards and forwards and oscillate in a locus. The path of the locus is directly related to a gear arm arrangement in contact with a gear rack that can be changed in amplitude and pitch via the offset holes in the gear.
The kinematic path of the tynes relative to the fixed evenly pitched horizontal screen bars causes the screenings to be pushed off the screen bars as the tynes reciprocate backwards and forwards. The tynes are supported and located in a spring loaded block.
The screening arrangement can further include a lifting arrangement to remove the screen for maintenance. The screen frame houses and seals the mechanical drive and slider arrangement from contamination and is tamperproof.
The electrical drive is a standard unit complete with overtorque clutch and position limit switches. The electrical drive motor is a standard actuator fitted to the end of the drive shaft completely sealed from the elements. Further as the drive train is an electrical unit it does not create environmental problems due to the oil leaking into the water stream as a hydraulic system does.
In accordance with a further aspect of the present invention, there is provided in a screening arrangement for screening a fluid comprising of a screening frame; horizontal but vertically stacked evenly pitched screen bars, a set of raking tynes to push and remove the captured screenings; and a drive motor for driving the raking tynes via the mechanical drive belt/chain through the slider blocks with the drive belt/chain completely sealed from the contaminated liquid. The second screen providing an increased hydraulic capacity of the incoming flow and reduction in hydraulic drive head to screen a higher flow across a screen without the contaminated liquid breaking the sides of the channel. This also reduces the extra capital infrastructure cost to augment the capacity of this unit process.